As shown in FIGS. 4(a) and 4(b), steel cords 13, 14 forming assembling members CDEF of a shoulder bladder used in making green tires are wrapped with a composition of rubber sheet and cord 11, 12 (hereinafter referred to as a cord-rubber composition) extending along the path defined by points G-F-E-D-C-F. The bladder includes body-ply layer 17, inflatable inner-rubber member 16 and cover-rubber layer 18. Rubber member 16, body-ply layer 17 and rubber layer 18 constitute the expandable part of the bladder which has a joint formed on the upper part thereof, as shown, for example, in FIG. 4(a). This prior bladder is manufactured by the sequential steps of FIGS. 5(a)-(f). The process illustrated in FIGS. 5(a)-(f) for manufacturing the prior bladder is as follows:
Green, uncured inner-rubber member 16, body-ply layer 17 and cover-rubber layer 18 constituting the bladder are adhered to each other in turn as illustrated in FIG. 5(a). End parts of member 16, as well as layers 17 and 18, are cut on the bias to obtain a green product. Valve 27 including stem 21 is bonded to the composite structure formed by inner rubber member 16 and layers 17 and 18, as illustrated in FIG. 5(a). One end of the slanted part of the green product is filed back on bending machine 39 to reach line K of machine 39, FIG. 5(b). Bonded stem 21 of valve 27 is folded so valve 27 of the green product extends outward for adhesion to line K to form pocket 24, FIG. 5(c).
In assembling the bladder portion extending between points CDEF, FIGS. 4(a) and 4(b), cord-rubber composition 11, 12 and steel cords 13, 14 are inserted into a cavity defined by points C'D'E'F' of body drum 30A and outer drum 31A, FIG. 5(d). Pocket 24 is turned out so valve 27 faces inward. Then parts 11-14 are inserted into body drum 30A and outer drum 31A (FIG. 5(d)) so the portion of the bladder between points C-F abuts the portions of drums 30A and 31A between points C'F'. Ring 33A is assembled thereto, as illustrated in FIG. 5(f). Rubber end portion 20 of the bladder (as illustrated in FIG. 2) abuts rubber end portion I'J', FIG. 5(f), of a folded portion of pocket 24. The surface of woven fabric 19 is wrapped to the proper width by inner tube 37. Then 140.degree.-160.degree. C. steam is injected to cure the green bladder.
However, the shoulder bladder manufacture by the method as described above has many defects, as follows:
First, since the portion of the bladder formed by metal cords 13, 14 is wrapped only by cord-rubber composition 11, 12, repeated expansion and deflation of the bladder during tire manufacturing frequently causes cracks and separation in the vicinity of point C', where stress is most cumulative. As shown in FIG. 1(b), inflation of shoulder bladder 1A while tire bead parts are formed and belt 8 is adhered to tread 9 causes air frequently to leak out through the separate portions of the bladder. Thereby, the position of a center line of a green tire before bladder inflation frequently differs from a center line of a manufactured green tire so there is poor adhesion of belt 8 and tread 9, resulting in a tire having poor uniformity.
The air leakage of the prior art bladder is frequently so slight that workers do not become aware of the fine crack and separation at point C of the bladder when the green tire is manufactured. The resulting tire thus frequently has an inferior rating and tire quality is greatly reduced.
Second, since the joint of the bladder body ply is disposed on the upper of the body ply, the expansion state of the bladder has a position as illustrated by dotted line 1'--1, FIG. 1(b) When the bead portion of the green tire is manufactured, the supporting force of the bladder from the interior of the bladder is fragile. Thereby a large quantity of air can get in through each position of the end portion 6A-1 of body ply 6A and a bead hump, causing great degradation to the tire quality. Furthermore, when belt 8 and tread 9 are adhered to the green tire, there is an increased probability of off-center adhesion due to the fragile supporting force of the bladder. This causes reduced tire quality and uniformity.
Third, since connection positions of the intermediate product formed of inner-rubber member 16, body-ply layer 17 and cover-rubber layer 18 constituting the bladder are only at one portion of an expanded tire circumference, the tire radius is not uniform.
Fourth, due to simultaneous curing of the surface of the bladder and the inner tube, when the inner tube is wound, a center portion in the transverse direction expands more than both ends during curing. The extent of expansion is determined by the differences of winding numbers and tension depending on each part in the transverse direction or each location along the bladder circumference. Thus, it is difficult for a bladder having equivalent transverse and circumferential dimensions to be manufactured because of dimensional variations of each bladder portion; the surface thereof can not be manufactured smoothly.
Accordingly, when a tire is manufactured by means of the molder utilizing the bladder obtained by the method described above, all qualities thereof, especially uniformity, are considerably reduced. This is because the tire quality depends on the dimensional deviations of the bladder assembled by the molder.
It is an object of the present invention to provide a new and improved method of preparing a tire molder shoulder bladder and more particularly to provide a method of preparing a bladder to overcome the structural defects of point C of the prior art occurring mostly due to cumulation of stress when the shoulder bladder is repeatedly expanded and deflated.
A further object is to provide a new and improved method of preparing a tire molder shoulder bladder capable of improving the quality of the tire and providing extended useful life thereof.
An additional object of the invention is to provide a new and improved method of preparing a tire molder shoulder bladder to prevent leakage of air filled in a green tire and to maintain pressure of the filled air during manufacture of the tire.
Another object of the invention is to provide a new and improved method of preparing a tire molder shoulder bladder used for making tires including one or more layers of radially disposed body-ply cords and two or more circumferential belts.
In accordance with a further aspect of the invention, a shoulder bladder for a tire molder is made by forming a first pocket by inserting a cord-rubber sheet superposed with a metal cord sheet into a recess of a drum assembly having a cavity. The recess is located on a bottom face of the cavity. The cord-rubber sheet is arranged so an end portion thereof extends out of the cavity. A second pocket is formed by locating on the drum assembly a structure including a rubber inner sheet superposed with a body-ply and a cover-rubber sheet so a bottom surface of the structure lies on a surface of the cavity and covers and contacts a sheet of the first pocket in the recess. The structure is folded on itself so an end of a top fold of the structure is secured to a bottom fold of the structure between the end portion of the cord-rubber sheet and a gas passage into the second pocket. The second pocket is manipulated so the recess is covered thereby. The end portion of the cord-rubber sheet is folded onto a top surface of the second pocket. A green bladder is thereby formed in the drum assembly. Cement is coated on an upper surface of the green bladder. A woven fabric is adhered tot he coated upper surface. A cover of the drum assembly is placed on the green bladder to cover the cavity to form a chamber where the materials forming the first and second pockets are located. Then air and steam are injected into the second pocket to cure the materials of the bladder so (a) the end portion of the cord-rubber sheet is bonded to the second pocket, (b) the superposed sheets forming the first and second pockets are bonded to each other and (c) the end of the structure is bonded to the bottom fold of the structure and the second pocket forms the expandable chamber of the bladder. A valve stem is adhered to the materials forming the second pocket prior to the drum cover being placed on the green bladder.